1. Field of the Disclosure
The present embodiments relate to semiconductor processing equipment, and in particular, to line charge volume pressure measurement.
2. Description of the Related Art
Semiconductor equipment used to fabricate semiconductor devices include various integrated systems. Depending on the application, there is often a need to deliver process gases to a reactor, e.g., when used to deposit a film over a semiconductor wafer. For instance, some reactors are used to perform atomic layer deposition (ALD), also known as atomic layer chemical vapor deposition (ALCVD). These deposition methods are used to produce very thin films that are highly conformal, smooth, and possess excellent physical properties. ALD uses volatile gases, solids, or vapors that are sequentially introduced (or pulsed) over a heated substrate.
Typically, a first precursor is introduced as a gas, which is absorbed (or adsorbed) into the substrate and the reactor chamber is cleared of the gaseous precursor. A second precursor is introduced as a gas, which reacts with the absorbed precursor to form a monolayer of the desired material. By regulating this sequence, the films produced by ALD are deposited a monolayer at a time by repeatedly switching the sequential flow of two or more reactive gases over the substrate. Thus, the supply of such gases and controlling the amount of gases introduced in various phases becomes important to achieving higher quality films.
In some implementations, a “charge volume” method is used for discretely metering precise bursts of chemistry into the process chamber of the reactor. For example, FIG. 1 shows a system 100 where a line charge volume (LCV) 102 is used to supply bursts of gas into the reactor 120. In a first life cycle state, the outlet valve 106 is closed, the inlet valve 104 is opened, and the line charge volume 102 is exposed to a flow of gas from an upstream source 130. This may be a pressure to which the line charge volume 102 ultimately equilibrates or a metered flow for a specified exposure time. The amount of chemistry in the line charge volume can be derived from suitable gas laws. If the chemistry conforms to the ideal gas law, then: m=PV/(R_m T).
In a second life cycle state, the inlet valve 104 is closed, and the outlet valve 106 is opened and the entire volume of the line charge volume 102 is exposed to the reactor 120 resulting in an outflow of gas from the line charge volume 102 to the reactor 120. As shown, the reactor 120 may include a showerhead 108 and a pedestal 112 that supports a substrate 110. The burst of gas from the line charge volume 102 is therefore delivered by the showerhead 108 to the processing region over the substrate 110. In the second state, it is desirable to have a very high conductance between the line charge volume 102 and the reactor 120.
In other configurations, a surface mount (IGS) versions of the charge volume (LCV) may be used, as shown in FIG. 2. In this configuration, a charge volume 122 and a capacitance diaphragm gauge (CDG) 124 is provided in tandem to define the LCV 102. This arrangement has two sub-optimum characteristics. First, the pressure reading, Pg, incurs a measurement error, where Pg=Pv−(m/C) and “m” is the molecular mass and “C” is the conductance. If exposed to an upstream pressure, then after the initial transient, the mass flow difference between the charge volume 122 and the CDG 124 will be zero. However, if a gas flow is used for a specified duration, the pressure reading error will be problematic.
Second, the single-ended volume formed by the cavity in the CDG 124 is difficult to purge as it represents a dead leg. As such, single-ended designs do not lend themselves to proper purging of residual atmospheric oxygen or water vapor. During a third lifecycle state of the charge volume 122, purge gases flow through the charge volume 122, but due to the proximity of the outlet port 105 to the inlet port 103, significant recirculation occurs and purging of the distal portions of the charge volume 122 is ineffective. This is similar to how a room can be cooled with air conditioning as air in a room is exchanged over time with the air flow entering and leaving the room vents. It is possible to purge this volume, but very inefficiently, as vast volumes of purge gas must be used and significant purge time is required.
It is in this context that disclosures arise.